The present invention relates generally to the fabrication of semiconductor devices, and the packaging of semiconductor devices. More specifically, this invention pertains to bonding pads, probing pads and solder bump pads on semiconductor devices and support structures for bonding pads.
Following the fabrication of the semiconductor devices on a wafer, each device (also known as a chip or die) is tested for functionality, or the wafers are “sorted”. Typically, a wafer having devices fabricated thereon is placed on a vacuum chuck. Electrical probes from a tester contact bonding pads formed on each of the devices to determine if individual devices are functional.
After the wafers are sorted, the wafer is cut and the devices are separated from one another using cutting tools known to those skilled in the art. The devices are then assembled onto a substrate using procedures known as die attach or die bonding.
Subsequent to the attachment of the devices to package substrates, electrical connections are made between the bonding pads on the devices and the electrical leads on the package. The electrical connections are made using different techniques including wire bonding, flip-chip bonding and tape-automated bonding. At least with respect to wire bonding, a bonding pad is subjected to a force applied directly to the bond that may damage underlying layers, materials, or components of a device.
In wire bonding techniques, such as thermo-compression, ultra-sonic bonding and thermo-sonic, a metal wire is pressed against a bond pad. Depending on the particular technique, the wire is heated and/or subjected to ultra-sonic vibrations to bond the metal wire to the bonding pad of the semiconductor device. The wire is then connected to electrical leads on the device package.
After the die attachment and wire bonding operations are completed, the device is then “packaged” into a plastic molded package or a ceramic package or similar package, depending upon the die size, package application and end-use.
The devices are subjected to thermal and mechanical stresses during electrical testing during wafer “sort” and subsequent assembly procedures. Damage to the device may be caused during wafer sorting, when the testing probes are pressed against the bonding pad. Probe testing involves the use of a probe needle or other contact devices which may damage and/or contaminate the bond pad. During the probing operation, bond pad metal may be deformed, “gouged” or “ploughed” into one or more regions of the bond pad, exposing underlying layers such as barrier materials, dielectrics and/or other conductors such as aluminum and copper, thus preventing a reliable electrical connection between the bond pad and the packaging pin during subsequent wire bonding. Moreover, the nature of the bond may be mechanically and metallurgically weak, leading to wire lift-off or a “non-stick” (no adherence) situation. This problem is exacerbated by the ever decreasing sizes of bond pad on which smaller wire bonds are formed, leaving very small regions where a sound wire bond is possible. Furthermore, during the wire bond operations, device layers underlying the bond pad are compressed and in some instances materials or components may be cracked and damaged. Dielectric cracking can occur and cracks can propagate through the layer to device components, which in turn may be damaged. Components may also be fabricated underneath the bond pad, and may be damaged directly from the force of the probe and wire bond operations.
Thus, a need exists to provide a bonding pad support structure that effectively protects device components that are disposed within the device directly under the pad in conjunction with minimizing the damage caused by probe testing and wire bonding or flip chip solder bumping. Such a support structure should isolate the damage within an underlying layer to an area subjacent the bonding pad. The structures of the present invention will prevent damage propagation to regions proximal to the bond pad. An added benefit is that the substructure will inhibit bond pad peeling that may result from underlying layer damage.